-----------------------------------------------------------------------------
-- JSON4Lua: JSON encoding / decoding support for the Lua language.
-- json Module.
-- Author: Craig Mason-Jones
-- Homepage: http://json.luaforge.net/
-- Version: 0.9.40
-- This module is released under the MIT License (MIT).
-- Please see LICENCE.txt for details.
--
-- USAGE:
-- This module exposes two functions:
-- encode(o)
-- Returns the table / string / boolean / number / nil / json.null value as a JSON-encoded string.
-- decode(json_string)
-- Returns a Lua object populated with the data encoded in the JSON string json_string.
--
-- REQUIREMENTS:
-- compat-5.1 if using Lua 5.0
--
-- CHANGELOG
-- 0.9.20 Introduction of local Lua functions for private functions (removed _ function prefix).
-- Fixed Lua 5.1 compatibility issues.
-- Introduced json.null to have null values in associative arrays.
-- encode() performance improvement (more than 50%) through table.concat rather than ..
-- Introduced decode ability to ignore /**/ comments in the JSON string.
-- 0.9.10 Fix to array encoding / decoding to correctly manage nil/null values in arrays.
-----------------------------------------------------------------------------
-----------------------------------------------------------------------------
-- Imports and dependencies
-----------------------------------------------------------------------------
local math = require('math')
local string = require("string")
local table = require("table")
local base = _G
-----------------------------------------------------------------------------
-- Module declaration
-----------------------------------------------------------------------------
module("json")
-- Public functions
-- Private functions
local decode_scanArray
local decode_scanComment
local decode_scanConstant
local decode_scanNumber
local decode_scanObject
local decode_scanString
local decode_scanWhitespace
local encodeString
local isArray
local isEncodable
-----------------------------------------------------------------------------
-- PUBLIC FUNCTIONS
-----------------------------------------------------------------------------
--- Encodes an arbitrary Lua object / variable.
-- @param v The Lua object / variable to be JSON encoded.
-- @return String containing the JSON encoding in internal Lua string format (i.e. not unicode)
function encode (v)
-- Handle nil values
if v==nil then
return "null"
end
local vtype = base.type(v)
-- Handle strings
if vtype=='string' then
return '"' .. encodeString(v) .. '"' -- Need to handle encoding in string
end
-- Handle booleans
if vtype=='number' or vtype=='boolean' then
return base.tostring(v)
end
-- Handle tables
if vtype=='table' then
local rval = {}
-- Consider arrays separately
local bArray, maxCount = isArray(v)
if bArray then
for i = 1,maxCount do
table.insert(rval, encode(v[i]))
end
else -- An object, not an array
for i,j in base.pairs(v) do
if isEncodable(i) and isEncodable(j) then
table.insert(rval, '"' .. encodeString(i) .. '":' .. encode(j))
end
end
end
if bArray then
return '[' .. table.concat(rval,',') ..']'
else
return '{' .. table.concat(rval,',') .. '}'
end
end
-- Handle null values
if vtype=='function' and v==null then
return 'null'
end
base.assert(false,'encode attempt to encode unsupported type ' .. vtype .. ':' .. base.tostring(v))
end
--- Decodes a JSON string and returns the decoded value as a Lua data structure / value.
-- @param s The string to scan.
-- @param [startPos] Optional starting position where the JSON string is located. Defaults to 1.
-- @param Lua object, number The object that was scanned, as a Lua table / string / number / boolean or nil,
-- and the position of the first character after
-- the scanned JSON object.
function decode(s, startPos)
startPos = startPos and startPos or 1
startPos = decode_scanWhitespace(s,startPos)
base.assert(startPos<=string.len(s), 'Unterminated JSON encoded object found at position in [' .. s .. ']')
local curChar = string.sub(s,startPos,startPos)
-- Object
if curChar=='{' then
return decode_scanObject(s,startPos)
end
-- Array
if curChar=='[' then
return decode_scanArray(s,startPos)
end
-- Number
if string.find("+-0123456789.e", curChar, 1, true) then
return decode_scanNumber(s,startPos)
end
-- String
if curChar==[["]] or curChar==[[']] then
return decode_scanString(s,startPos)
end
if string.sub(s,startPos,startPos+1)=='/*' then
return decode(s, decode_scanComment(s,startPos))
end
-- Otherwise, it must be a constant
return decode_scanConstant(s,startPos)
end
--- The null function allows one to specify a null value in an associative array (which is otherwise
-- discarded if you set the value with 'nil' in Lua. Simply set t = { first=json.null }
function null()
return null -- so json.null() will also return null ;-)
end
-----------------------------------------------------------------------------
-- Internal, PRIVATE functions.
-- Following a Python-like convention, I have prefixed all these 'PRIVATE'
-- functions with an underscore.
-----------------------------------------------------------------------------
--- Scans an array from JSON into a Lua object
-- startPos begins at the start of the array.
-- Returns the array and the next starting position
-- @param s The string being scanned.
-- @param startPos The starting position for the scan.
-- @return table, int The scanned array as a table, and the position of the next character to scan.
function decode_scanArray(s,startPos)
local array = {} -- The return value
local stringLen = string.len(s)
base.assert(string.sub(s,startPos,startPos)=='[','decode_scanArray called but array does not start at position ' .. startPos .. ' in string:\n'..s )
startPos = startPos + 1
-- Infinite loop for array elements
repeat
startPos = decode_scanWhitespace(s,startPos)
base.assert(startPos<=stringLen,'JSON String ended unexpectedly scanning array.')
local curChar = string.sub(s,startPos,startPos)
if (curChar==']') then
return array, startPos+1
end
if (curChar==',') then
startPos = decode_scanWhitespace(s,startPos+1)
end
base.assert(startPos<=stringLen, 'JSON String ended unexpectedly scanning array.')
object, startPos = decode(s,startPos)
table.insert(array,object)
until false
end
--- Scans a comment and discards the comment.
-- Returns the position of the next character following the comment.
-- @param string s The JSON string to scan.
-- @param int startPos The starting position of the comment
function decode_scanComment(s, startPos)
base.assert( string.sub(s,startPos,startPos+1)=='/*', "decode_scanComment called but comment does not start at position " .. startPos)
local endPos = string.find(s,'*/',startPos+2)
base.assert(endPos~=nil, "Unterminated comment in string at " .. startPos)
return endPos+2
end
--- Scans for given constants: true, false or null
-- Returns the appropriate Lua type, and the position of the next character to read.
-- @param s The string being scanned.
-- @param startPos The position in the string at which to start scanning.
-- @return object, int The object (true, false or nil) and the position at which the next character should be
-- scanned.
function decode_scanConstant(s, startPos)
local consts = { ["true"] = true, ["false"] = false, ["null"] = nil }
local constNames = {"true","false","null"}
for i,k in base.pairs(constNames) do
--print ("[" .. string.sub(s,startPos, startPos + string.len(k) -1) .."]", k)
if string.sub(s,startPos, startPos + string.len(k) -1 )==k then
return consts[k], startPos + string.len(k)
end
end
base.assert(nil, 'Failed to scan constant from string ' .. s .. ' at starting position ' .. startPos)
end
--- Scans a number from the JSON encoded string.
-- (in fact, also is able to scan numeric +- eqns, which is not
-- in the JSON spec.)
-- Returns the number, and the position of the next character
-- after the number.
-- @param s The string being scanned.
-- @param startPos The position at which to start scanning.
-- @return number, int The extracted number and the position of the next character to scan.
function decode_scanNumber(s,startPos)
local endPos = startPos+1
local stringLen = string.len(s)
local acceptableChars = "+-0123456789.e"
while (string.find(acceptableChars, string.sub(s,endPos,endPos), 1, true)
and endPos<=stringLen
) do
endPos = endPos + 1
end
local stringValue = 'return ' .. string.sub(s,startPos, endPos-1)
local stringEval = base.loadstring(stringValue)
base.assert(stringEval, 'Failed to scan number [ ' .. stringValue .. '] in JSON string at position ' .. startPos .. ' : ' .. endPos)
return stringEval(), endPos
end
--- Scans a JSON object into a Lua object.
-- startPos begins at the start of the object.
-- Returns the object and the next starting position.
-- @param s The string being scanned.
-- @param startPos The starting position of the scan.
-- @return table, int The scanned object as a table and the position of the next character to scan.
function decode_scanObject(s,startPos)
local object = {}
local stringLen = string.len(s)
local key, value
base.assert(string.sub(s,startPos,startPos)=='{','decode_scanObject called but object does not start at position ' .. startPos .. ' in string:\n' .. s)
startPos = startPos + 1
repeat
startPos = decode_scanWhitespace(s,startPos)
base.assert(startPos<=stringLen, 'JSON string ended unexpectedly while scanning object.')
local curChar = string.sub(s,startPos,startPos)
if (curChar=='}') then
return object,startPos+1
end
if (curChar==',') then
startPos = decode_scanWhitespace(s,startPos+1)
end
base.assert(startPos<=stringLen, 'JSON string ended unexpectedly scanning object.')
-- Scan the key
key, startPos = decode(s,startPos)
base.assert(startPos<=stringLen, 'JSON string ended unexpectedly searching for value of key ' .. key)
startPos = decode_scanWhitespace(s,startPos)
base.assert(startPos<=stringLen, 'JSON string ended unexpectedly searching for value of key ' .. key)
base.assert(string.sub(s,startPos,startPos)==':','JSON object key-value assignment mal-formed at ' .. startPos)
startPos = decode_scanWhitespace(s,startPos+1)
base.assert(startPos<=stringLen, 'JSON string ended unexpectedly searching for value of key ' .. key)
value, startPos = decode(s,startPos)
object[key]=value
until false -- infinite loop while key-value pairs are found
end
--- Scans a JSON string from the opening inverted comma or single quote to the
-- end of the string.
-- Returns the string extracted as a Lua string,
-- and the position of the next non-string character
-- (after the closing inverted comma or single quote).
-- @param s The string being scanned.
-- @param startPos The starting position of the scan.
-- @return string, int The extracted string as a Lua string, and the next character to parse.
function decode_scanString(s,startPos)
base.assert(startPos, 'decode_scanString(..) called without start position')
local startChar = string.sub(s,startPos,startPos)
base.assert(startChar==[[']] or startChar==[["]],'decode_scanString called for a non-string')
local escaped = false
local endPos = startPos + 1
local bEnded = false
local stringLen = string.len(s)
repeat
local curChar = string.sub(s,endPos,endPos)
-- Character escaping is only used to escape the string delimiters
if not escaped then
if curChar==[[\]] then
escaped = true
else
bEnded = curChar==startChar
end
else
-- If we're escaped, we accept the current character come what may
escaped = false
end
endPos = endPos + 1
base.assert(endPos <= stringLen+1, "String decoding failed: unterminated string at position " .. endPos)
until bEnded
local stringValue = 'return ' .. string.sub(s, startPos, endPos-1)
local stringEval = base.loadstring(stringValue)
base.assert(stringEval, 'Failed to load string [ ' .. stringValue .. '] in JSON4Lua.decode_scanString at position ' .. startPos .. ' : ' .. endPos)
return stringEval(), endPos
end
--- Scans a JSON string skipping all whitespace from the current start position.
-- Returns the position of the first non-whitespace character, or nil if the whole end of string is reached.
-- @param s The string being scanned
-- @param startPos The starting position where we should begin removing whitespace.
-- @return int The first position where non-whitespace was encountered, or string.len(s)+1 if the end of string
-- was reached.
function decode_scanWhitespace(s,startPos)
local whitespace=" \n\r\t"
local stringLen = string.len(s)
while ( string.find(whitespace, string.sub(s,startPos,startPos), 1, true) and startPos <= stringLen) do
startPos = startPos + 1
end
return startPos
end
--- Encodes a string to be JSON-compatible.
-- This just involves back-quoting inverted commas, back-quotes and newlines, I think ;-)
-- @param s The string to return as a JSON encoded (i.e. backquoted string)
-- @return The string appropriately escaped.
function encodeString(s)
s = string.gsub(s,'\\','\\\\')
s = string.gsub(s,'"','\\"')
s = string.gsub(s,"'","\\'")
s = string.gsub(s,'\n','\\n')
s = string.gsub(s,'\t','\\t')
return s
end
-- Determines whether the given Lua type is an array or a table / dictionary.
-- We consider any table an array if it has indexes 1..n for its n items, and no
-- other data in the table.
-- I think this method is currently a little 'flaky', but can't think of a good way around it yet...
-- @param t The table to evaluate as an array
-- @return boolean, number True if the table can be represented as an array, false otherwise. If true,
-- the second returned value is the maximum
-- number of indexed elements in the array.
function isArray(t)
-- Next we count all the elements, ensuring that any non-indexed elements are not-encodable
-- (with the possible exception of 'n')
local maxIndex = 0
for k,v in base.pairs(t) do
if (base.type(k)=='number' and math.floor(k)==k and 1<=k) then -- k,v is an indexed pair
if (not isEncodable(v)) then return false end -- All array elements must be encodable
maxIndex = math.max(maxIndex,k)
else
if (k=='n') then
if v ~= table.getn(t) then return false end -- False if n does not hold the number of elements
else -- Else of (k=='n')
if isEncodable(v) then return false end
end -- End of (k~='n')
end -- End of k,v not an indexed pair
end -- End of loop across all pairs
return true, maxIndex
end
--- Determines whether the given Lua object / table / variable can be JSON encoded. The only
-- types that are JSON encodable are: string, boolean, number, nil, table and json.null.
-- In this implementation, all other types are ignored.
-- @param o The object to examine.
-- @return boolean True if the object should be JSON encoded, false if it should be ignored.
function isEncodable(o)
local t = base.type(o)
return (t=='string' or t=='boolean' or t=='number' or t=='nil' or t=='table') or (t=='function' and o==null)
end